A study on unsteady fluid-dynamic force characteristics of a pitching wing with leading edge protuberance

Abstract

We conducted a study on unsteady characteristics of fluid-dynamic force acting on a pitching NACA0012 wing with linear leading edge (Baseline) and with leading edge protuberance (Wave) in low Reynolds number region (Re =4.32×104) for the development of fish-type autonomous underwater vehicle. To investigate the effect of pitching motion on the fluid-dynamic force, force measurement and flow visualization were conducted by using a wind tunnel. In the case of Baseline, increase in pitching frequency and amplitude produced higher lift force than the quasi-steady one in upstroke phase. On the other hand, in downstroke phase, the lift force decreased and become lower than the quasi-steady state. However, at large pitching amplitude such as 15° where the rapid decrease in lift was observed at the end of downstroke phase, the lift change was close to the quasi-steady one. Flow visualization showed that the increase in lift force at upstroke phase was caused by separation control effect of the upstroke motion. In the case of Wave, although the same characteristics of unsteady fluid-dynamic forces as the Baseline case were observed, higher average lift and smaller lift fluctuation than the Baseline case which caused by the separation control effect of leading edge protuberance were confirmed regardless of the pitching conditions. Furthermore, the 2-dimentional potential flow analysis revealed that the effects of unsteady lift and drag forces attributed to the potential flow were considerably small compared with one by flow separation.

Keywords

• leading edge protuberance
• pitching motion
• naca0012
• low reynolds number
• unsteady lift